Method for the synthesis of a stable heteroatom analog of trimethylenemethane

Russian Chemical Bulletin - A procedure was developed for the synthesis of the kinetically stable nitroxide...     

Vector model of electron spin echo envelope modulation due to nuclear hyperfine and zeeman interactions

The transverse electron spin magnetization of a paramagnetic center with effective spinS=1/2 interacting with nonquadrupolar nuclei may be presented as a function of pairs of nuclei magnetization vectors which precess around the effective magnetic field directions. Each vector of the pair starts its precession perpendicular to both effective fields. The free induction decay (FID) signal is proportional to the scalar product of the vectors for nuclear spinI=1/2. The electron spin echo (ESE) signal can be described with two pairs of magnetization vectors. The ESE shape is not equal to two back-to-back FID signals except in the absence of ESE envelope modulation. A recursion relation is obtained which allows calculation of ESE signals for larger nuclear spins in the absence of nuclear quadrupole interaction. This relation can be used to calculate the time course of the ESE signal for arbitrary nuclear spins as a function of the nuclear magnetization vectors. While this formalism allows quantitative calculation of modulation from nuclei, it also provides a qualitative means of visualizing the modulation based on simple magnetization vectors.     

Formation of the pulsed electron-electron double resonance signal in the case of a finite amplitude of microwave fields

A theoretical study of the effect of microwave (MW) fields of finite amplitude on the process of pulsed electron-electron double resonance (PELDOR) signal formation is carried out. It is shown that the behavior of the experimentally observed values can be described by four vectors of partial magnetizations whose motion is reduced to precession in effective magnetic fields. In the case of strong spin-spin interaction, the PELDOR effect can be observed when a sufficiently powerful MW field is applied at pumping frequency to affect both components of the Pake doublet. The possibility of a “two-frequency” spin echo to appear under the action of two pulses with different carrier frequencies in the system where the inhomogeneous broadening of the electron spin resonance line contour is mainly determined by the dipole-dipole interaction is demonstrated.     

Visualization of distance distribution from pulsed double electron-electron resonance data

Double electron-electron resonance (DEER), also known as pulsed electron-electron double resonance (PELDOR), is a time-domain electron paramagnetic resonance method that can measure the weak dipole-dipole interactions between unpaired electrons. DEER has been applied to discrete pairs of free radicals in biological macromolecules and to clusters containing small numbers of free radicals in polymers and irradiated materials. The goal of such work is to determine the distance or distribution of distances between radicals, which is an underdetermined problem. That is, the spectrum of dipolar interactions can be readily calculated for any distribution of free radicals, but there are many, quite different distributions of radicals that could produce the same experimental dipolar spectrum. This paper describes two methods that are useful for approximating the distance distributions for the large subset of cases in which the mutual orientations of the free radicals are uncorrelated and the width of the distribution is more than a few percent of its mean. The first method relies on a coordinate transformation and is parameter-free, while the second is based on iterative least-squares with Tikhonov regularization. Both methods are useful in DEER studies of spin-labeled biomolecules containing more than two labels.